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 A276645 Numbers n such that A002088(n) is a triangular number. 0
 0, 1, 4, 5, 9, 19, 148, 209, 404, 652, 763, 1739, 2790, 9551, 11117, 13173, 25641, 170003, 181927, 519900, 3253342, 4816257, 7103608, 8269588, 64261168, 177847445, 294878941, 819667577, 844965349, 2944185248 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Corresponding triangular numbers are 0, 1, 6, 10, 28, 120, 6670, 13366, 49770, 129286, 177310, ... LINKS EXAMPLE 9 is a term because A002088(9) = 1+1+2+2+4+2+6+4+6 = 28 = 1+2+3+4+5+6+7. PROG (PARI) lista(nn) = {print1(st = 0, ", "); for(n=1, nn, st += eulerphi(n); if (ispolygonal(st, 3), print1(n, ", "))); } \\ Michel Marcus, Sep 09 2016 CROSSREFS Cf. A000217, A002088. Sequence in context: A280225 A153058 A216225 * A293282 A240926 A041032 Adjacent sequences:  A276642 A276643 A276644 * A276646 A276647 A276648 KEYWORD nonn,more AUTHOR Altug Alkan, Sep 09 2016 EXTENSIONS More terms from Michel Marcus, Sep 09 2016 a(25)-a(30) from Lars Blomberg, Oct 15 2016 STATUS approved

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Last modified April 14 01:49 EDT 2021. Contains 342941 sequences. (Running on oeis4.)